Timothy F. Geithner was questioned sharply on Wednesday about the rate-rigging scandal that has consumed the banking industry, as lawmakers at a House hearing asked why he had failed to thwart wrongdoing during the financial crisis.

Republicans took aim at Mr. Geithner for, in their view, going easy on Wall Street despite knowing that some banks had been trying to manipulate a key interest rate. When he ran the Federal Reserve Bank of New York in 2008, Mr. Geithner advocated broad reforms to the rate-setting process rather than curbing the bad behavior at specific banks.

Mr. Geithner, now the Treasury secretary, also acknowledged on Wednesday that he had never alerted federal prosecutors to the wrongdoing. The revelation further stoked the ire of Republicans, including some regular detractors of Mr. Geithner.

“It appears you treated it as almost a curiosity, or something akin to jaywalking, as opposed to highway robbery,” said Jeb Hensarling, Republican of Texas.

The hearing before the House Financial Services Committee was the latest forum to scrutinize regulators’ role in the rate manipulation scandal. Lawmakers have pressed the New York Fed and its British counterparts to explain why illegal actions went unchecked for years.

Libor Explained

But Mr. Geithner escaped relatively unscathed from the more than two-hour hearing. Even as Republicans denounced Mr. Geithner for his actions as president of the New York Fed, many Democrats rushed to his defense. Barney Frank, a Massachusetts Democrat, declared that it was the banks, not regulators, that “grievously misbehaved.”

Mr. Geithner, who on Wednesday was also asked to outline the broader state of Wall Street regulation, challenged his Republican critics. In testimony, Mr. Geithner said that he was “very concerned” about the interest rate problem and he had promptly notified other regulators about his worries.

British authorities who oversee the rate, he said, failed to heed his warnings.

The controversy centers on the London interbank offered rate, or Libor, a measure of how much banks charge to lend to one another. Libor, lawmakers observed, is entwined in the financial system as a benchmark for trillions of dollars in mortgages and other loans.

A global investigation into more than a dozen big banks has now called into question the integrity of the important rate. Last month, Barclays struck a $450 million settlement with American and British authorities over accusations that it had undermined Libor to bolster its trading profits and project a strong image of its health, the first action to stem from the multiyear inquiry.

On Wednesday, the European Commission announced plans to make the manipulation of benchmark interest rates a criminal offense.

Barclays on Wednesday also disclosed the resignation of Alison Carnwath, head of the firm’s compensation board committee, in the latest shake-up at the beleaguered bank. She is leaving for undisclosed personal reasons. The firm’s chairman, Marcus Agius, and chief executive, Robert E. Diamond Jr., have agreed to step down amid the inquiries into Libor.

The New York Fed learned in April 2008 that Barclays had been artificially depressing its rates. “We know that we’re not posting, um, an honest” rate, a Barclays employee told a New York Fed official.

Mr. Geithner said he was not then aware of “that specific conversation.”

But that same day, New York Fed officials wrote in a weekly internal memo that the problem was widespread. “Our contacts at Libor contributing banks have indicated a tendency to underreport actual borrowing costs,” New York Fed officials wrote. At the time, high borrowing costs were a sign of poor health.

Even after discovering that banks were manipulating Libor, the New York Fed pursued a somewhat passive approach. When Mr. Geithner briefed other American regulators on Libor in May 2008, he did not disclose the specific wrongdoing at Barclays.

Republicans also seized on Mr. Geithner’s acknowledgment that he had not notified the Justice Department about the illegal behavior. The Justice Department, he explained, did not belong to the group of regulators that were focused on Libor.

In response to the criticism, Mr. Geithner pointed to his past efforts to reform Libor. He noted the New York Fed had repeatedly pressed for an overhaul of the rate-setting process. In a June 2008 e-mail to the Bank of England, the country’s central bank, Mr. Geithner recommended that British officials “eliminate incentive to misreport” Libor.

The New York Fed then advocated fixes more forcefully than its British counterparts, records show. British authorities later adopted only some of Mr. Geithner’s recommendations.

“We gave them very specific detailed changes,” Mr. Geithner said, adding that “if more of those would have been adopted sooner, you would have limited the risk.”

But Randy Neugebauer, Republican of Texas, questioned why the New York Fed had focused on policy solutions rather than the overt legal violations. “If they were having structural problems, then I think your e-mail was appropriate,” said Mr. Neugebauer, who is leading an investigation into how the New York Fed had handled the Libor scandal. “But what was being disclosed here was fraud.”

Ultimately, Mr. Geithner said, responsibility rests with the British regulators. “We felt, and I still believe this, it was really going to be on them to fix this.”

Democrats echoed his argument. “I for one am not part of the ‘blame America first’ crowd,” said Brad Sherman, Democrat of California.

“There’s been an effort to blame you for all of this,” said Mr. Frank, the ranking Democrat on the committee. But that is a surprising stance for Republicans, he said, given their general aversion to regulatory authority.